Multi-carrier (multiple carriers) technology may be called a carrier aggregation technology. The multi-carrier technology provides an effect as if using a frequency bandwidth on a broadband logically in a manner of physically bundling a plurality of carriers together in frequency domain to support an extended bandwidth, unlike a conventional wireless communication system that uses a single carrier only in uplink/downlink (UL/DL).
Meanwhile, uplink (UL) control information may consist of scheduling request, acknowledgement/non-acknowledgement (ACK/NACK) for a downlink (DL) transmission, a downlink channel state information and the like. In a single-carrier system according to a related art, a user equipment receives DL data on a single carrier and then transmits an ACK (acknowledgement) signal, i.e., an ACK/NACK signal in response to the received DL data.